Resonant power converters are uniquely suited for applications requiring a power supply with high power density. High power density is achievable in a resonant power converter because the cyclic energy storage components of the power supply for a given power capability can be significantly smaller at very high frequencies.
Resonant converters operate by utilizing a series tuned reactive circuit as a reactive divider in combination with a load network. The output load voltage is inversely proportional to the switching frequency. Frequency of switching is always above a minimum threshold so that the series tuned network is an inductive impedance. If the load decreases in value and the input line voltage increases the frequency of operation is increased to increase the reactive division ratio to maintain regulation of the output voltage. As the load decreases further the frequency increases to a value at which high component losses result in a considerable loss in efficiency in the converter.
The need to restrain the range of frequency variation limits the load range that can be accepted, if operational efficiency is to be maintained. This limitation of acceptable load range is particularly aggravated when the load demands a wide range of output currents.